1. Field of the Invention
The present invention relates to a nonmagnetic black toner used for the development of a latent image formed in electrophotography, electrostatic recording method, electrostatic printing method or the like.
2. Discussion of the Related Art
Conventionally, carbon blacks have been used as a black colorant for a toner. However, the carbon blacks have some defects such that the volume specific resistance is low, so that triboelectric charges required for development cannot be maintained, whereby a sufficient degree of blackness cannot be obtained. In addition, there are also pointed out some problems in safety hygiene. Therefore, various composite oxides have been proposed as black colorants used in place of carbon black (Japanese Patent Laid-Open No. 2000-10344 (U.S. Pat. No. 6,130,017) and Japanese Patent Laid-Open No. Hei 9-25126.
On the other hand, recently, similar to the widespread trends in plain paper copy machines (PPC), there has been a remarkable progress in laser beam printers (LBP). In the case of the PPC, the development is carried out by forming an electrostatic latent image carrying electric charges on a photoconductor, and changing its surface potential by the intensity of the light source, thereby changing the image tone (charged area development). By contrast, in the case of LBP, since a latent image not having electric charges is formed by two-step of on-and-off, the area coverage modulation by the number of halftones is carried out (discharged area development, i.e. reversal development).
Therefore, in the case of reversal development, evenness of the individual toner particles are strongly demanded. However, since the composite oxide has low dispersibility, there are generated “empty particles” in which no colorant is included in a toner comprising the composite oxide as a colorant, thereby lowering the clarity of the fixed images.
An object of the present invention is to provide a nonmagnetic black toner comprising a black colorant useful for reversal development, and containing substantially no empty particles.
These and other objects of the present invention will be apparent from the following description.